Wind power generator systems, along with solar power generator systems, are catching great attention as a means of producing renewable energy. Wind power generator systems generate electric power by rotationally driving a blade(s) with the aid of wind force and rotating a rotor of an electrical energy generator using the energy generated by the rotational driving of the blade. During power-generating operation, these systems control the pitch angle, rotational angle in a horizontal direction, and other parameters of the blade, according to wind direction and wind speed, to use the force of the wind more efficiently for power generation. The control devices that perform wind turbine control functions including such control are called auxiliary machines, and a power source for driving the auxiliary machines is generally covered by the electric power supplied from power systems.
In the case where as discussed above, the driving power source for auxiliary machines is covered by the electric power supplied from a power system, a significant drop in the voltage of the power system due to a lightning strike, a grounding fault, or the like, will render unobtainable the driving power source for the auxiliary machines, resulting in continued driving thereof being impossible. If the driving of the auxiliary machines cannot be continued, the power-generating operation itself will also be difficult to continue. However, if the wind power generator system, the power supply source, becomes unable to generate power with each occurrence of a lightning strike, a grounding fault, or the like, this will make stabilized supply of power difficult. For this reason, wind power generator systems are desired to have an LVRT (Low Voltage Ride Through) function that also makes the generator system resistant to such a voltage drop at the power system side.
In connection with this, Patent Documents 1 and 2, for example, describe wind turbine generators that implement such an LVRT function as above.
It is described in Patent Document 1 that if such voltage dips as discussed above occur in a power system, uninterruptible power supplies (UPS's) are used to cover the power required for auxiliary machines.
Patent Document 2 describes a wind turbine power generator system including an emergency power supply system equipped with an emergency power generator and an emergency changeover switch, the generator system being configured so that if an unusual event of a system voltage dip occurs, the emergency changeover switch has its operating position changed to power a pitch control mechanism, a main control device, and the like, from the emergency power supply system.